KENNEDY SPACE CENTER, FLA. - Space Shuttle Discovery remains on the pad the day after the Shuttle?s launch on Return to Flight mission STS-114 was scrubbed. The Rotating Service Structure has been closed. At left is the 290-foot-tall water tower that holds 300,000 gallons of water, part of the sound suppression system during a launch. Above the Shuttle at right is the 80-foot lightning mast. The July 13 mission was scrubbed when a low-level fuel cut-off sensor for the liquid hydrogen tank inside the External Tank failed a routine prelaunch check during the countdown July 13, causing mission managers to scrub Discovery's first launch attempt. The sensor protects the Shuttle's main engines by triggering their shutdown in the event fuel runs unexpectedly low. The sensor is one of four inside the liquid hydrogen section of the External Tank (ET).